Over the past few years, various multi-access systems have been developed in response to user demands for systems that can offer ready access to a wide variety of real-time or delay critical packet switched network services. Examples of these services include voice over Internet protocol (VoIP), cable TV or telephony services.
In the vast majority of conventional multi-access systems which provide these types of services, transmission resources are typically assigned to users during periods they actually have information to transmit. For example, in time assigned speech interpolation (TASI) systems where at any given time, multiple users engaged in different audio conversations share a limited number of transmission channels, channels are only allocated to each user during active speech segments or bursts.
When a user initiates a speech segment in these systems, the speech segment is received at a statistical multiplexor which proceeds to allocate channels to transmit the speech segment. When the user enters periods of silence or inactivity, the channels allocated are substantially reduced and typically re-allocated to other users or provisioned for control transmissions. This dynamic allocation of the available transmission resources also known as statistical multiplexing is commonly used in multi-access systems to increase traffic capacity and more importantly, to maximize the use of transmission resources which are often limited.
When a user initiates a new speech segment and switches from a state of inactivity to a state of activity, there is usually some delay before the necessary transmission resources can be allocated. This delay may result in situations where at the beginning of each speech segment, information is sent to a concentrator or multiplexor and is ready to be transmitted but the channel resources necessary for its transmission are not yet available. In conventional systems, the information ready to be transmitted before channel resources become available is typically discarded.
However, because information is discarded, speech segments are clipped at the onset causing information contained therein to be lost. In some systems, it has been shown that segments can be clipped for up to 40 milliseconds. Such clipping can severely disrupt user conversations, particularly where frequent pauses and silence periods occur.
This problem can also arise in multi-access wireless systems providing the same or other types of real-time services. In a multi-access wireless system providing audio services for example, delays in obtaining the appropriate radio resources are inevitable. Because of these delays, video segments or bursts may be clipped. Again, this clipping may as a result substantially damage or distort entire transmissions.
In order to avoid clipping, some multi-access systems delay transmission until channel resources become available. Unfortunately, adding delays to avoid clipping may be inappropriate. For example, adding delays during an audio conversation affect the entire dynamic of the conversation. In wireless systems, these delays considerably disrupt voice transmissions and reduce quality, sometimes below what is considered acceptable.
Therefore, when allocating radio resources in multi-access systems for the transmission of real-time or delay critical data such as, for example, audio or video information, it would be desirable to reduce delays and eliminate clipping to prevent transmission disruptions.